1. Field of the Invention
The present invention relates to a clamping device of an injection molding machine in which an adaptor plate is attached between a mold attachment surface of a platen and a mold fixed to this platen, and which controls a temperature of this adaptor plate.
2. Description of the Related Art
In a clamping device of an injection molding machine, a fixed platen and a rear platen are generally coupled by a plurality of tie bars. The fixed platen is fixed to tie bars by fixing platen nuts provided on a tie bar side. Similarly, the rear platen is also fixed to the tie bars by rear platen nuts provided on the tie bar side. The rear platen nuts are rotatably attached around the centers of tie bar shafts, so that, by rotating the rear platen nuts to move the rear platen forward and backward with respect to the fixed platen, it is possible to adjust the thickness of a mold.
Although most of injection molding machines use four tie bars, when stretch amounts of these four tie bars are different, the lengths of the tie bars differ and a parallelism (platen parallelism) of a mold attachment surface of the fixed platen and a mold attachment surface of a movable platen does not match in some cases. Hence, generally, clamping amounts of rear platen nuts are adjusted to precisely adjust the stretch amounts of the tie bars and the platen parallelism. However, the clamping amounts of the rear platen can be adjusted only before molding, and cannot be adjusted during molding.    (1) JP 2-75499 A and JP 2006-347078 A disclose techniques of attaching a heater to each tie bar, fluctuating a stretch amount of each tie bar byway of thermal expansion and adjusting a tie bar balance.
However, although this technique can adjust the tie bar balance and the platen parallelism by changing temperatures of tie bars and adjusting the stretch amounts of the tie bars, the final purpose of injection molding is to uniformly distribute a clamping force to an entire mold, and changing the temperatures of the tie bars and stretching the tie bars are indirect means and not direct one. Further, a center portion of the mold and the tie bars are slightly distant, and therefore there is a problem that it is not possible to make a mold surface pressure uniform even by adjusting the stretch amounts of the tie bars.    (2) JP 62-264921 A, JP 2000-271981 A and JP 2006-212980 A disclose techniques of canceling a difference between temperatures of sites of a platen and maintaining a fixed temperature over the entire platen.
However, this technique makes the temperature uniform over the entire platen, and, therefore, even when a tie bar balance is lost or the platen parallelism does not match due to, for example, a difference between stretch amounts of tie bars, the entire temperature is adjusted while the balance is lost and the parallelism does not match and there is a problem that it is not possible to adjust the tie bar balance or the platen parallelism.